What does testing or monitoring “as necessary” mean per 1910.146(d)(5)(ii) to decide if the acceptable entry conditions are being maintained?

The standard does not have specific frequency rates because of the performance oriented nature of the standard and the unique hazards of each permit space. However, there will always be, to some degree, testing or monitoring during entry operations which is reflective of the atmospheric hazard. The employer must determine the degree and the frequency of testing or monitoring. Some of the factors that affect frequency are:

• Results of test allowing entry.
• The regularity of entry (daily, weekly, or monthly).
• The uniformity of the permit space (the extent to which the configuration, use, and contents vary).
• The documented history of previous monitoring activities.
• Knowledge of the hazards which affect the permit space as well as the historical experience gained from monitoring results of previous entries.

Knowledge and recorded data from successive entries (such as ventilation required to maintain acceptable entry conditions) may be used to document changes in monitoring frequency.